Drive mechanisms of the general type to which the present invention relate are not new per se. These drive mechanisms typically comprise a pump rotor mounted in a pump chamber which is surrounded by a pump cover having an axially projecting shoulder end having a bore for the pump rotor. A shaft is connected at its inner end to the pump rotor and by a coupling element to the drive wheel, the shaft being supported in an inner bearing seated in the housing bore, while the drive wheel is supported in an external bearing. In accordance with a prior known mechanism of the type shown in West German Patent Application No. 3 716 098.2, the inner ring of the outer bearing providing the radial and axial support is seated on a cylindrical lateral surface section of the axially projecting shoulder of the pump cover.
The drive mechanism described above has several disadvantages and drawbacks. For example, in the design shown in the West Germany application, there is a frequent need to tension the drive belt by means of an eccentric adjustment of the drive wheel which is rather awkward and difficult to do. For example, when the drive wheel is shifted by adjusting the pump cover after the appropriate mounting screws have been loosened, the shaft is also shifted eccentrically along with the pump rotor. In other words, the pump rotor runs eccentrically in the pump chamber which creates problems with the seals and is instrumental in detracting from peak performance. Furthermore, there is only a limited range of eccentricity available for adjustments.